The veterinary drug blamed for killing South Asia's vultures has been banned by the Indian government.

Conservationists say that the population of three species of Asian vultures has fallen by 97% in 12 years, and they are now at risk of extinction.

The livestock painkiller diclofenac, consumed by vultures when they eat a carcass, has been blamed for the fall.

Studies in India, Pakistan and Nepal have found extensive evidence of diclofenac in dead vultures.

Captive breeding programmes

"The decline of three raptor species of vulture across South Asia has been absolutely catastrophic," said Debbie Pain, head of international research at the UK's Royal Society for the Protection of Birds (RSPB).

"Even though diclofenac has now been banned, it will take some time before the drug is removed from the food chain.

"It is essential that the authorities in India carry on with vulture captive breeding programmes if several species of the bird are to survive," she said.

Once very common, vultures are now becoming rare (Image: Asad Rahmani)

Vultures have an important ecological role in the Asian environment, where they have been relied upon for millennia to clean up and remove dead livestock and even human corpses.

Dr Pain and other ornithologists have warmly welcomed the ban imposed by the government, despite some initial scepticism in India that the drug could be the cause of the birds' decline.

Vultures hold a critical position in the food chain and are renowned for their ceaseless scavenging.

But their once-abundant numbers have been in decline for more than a decade.

In 1999, the Bombay Natural History Society noted a 97% drop in the Oriental white-backed vulture (Gyps bengalensis) population at the Keoladeo National Park in the state of Rajasthan.

Kidney failure

Today the bird is considered to be "critically endangered", as are long-billed (Gyps indicus) and slender-billed (Gyps tenuirostris) vultures which have been through a similar decline.

The decision to ban diclofenac was taken last week during a meeting of the government-affiliated National Board for Wildlife.

The decline of three raptor species of vulture across South Asia has been absolutely catastrophic

Debbie Pain, RSPB

Indian Prime Minister Manmohan Singh endorsed the board's recommendation to phase out the veterinary use of the drug over the next six months.

Mr Singh said that he expected the ministries of health and animal husbandry to promote options to replace the drug such as ketoprofen and meloxicam. Both are believed to be less toxic to vultures.

Last year, a study in the Journal of Applied Ecology showed how only a little exposure is needed to knock back vulture numbers.

The birds succumb to kidney failure and visceral gout when they eat a dead animal that has been treated with diclofenac, an anti-inflammatory drug.

Early signs that the raptors are affected can be seen from the way they hang their heads down to their feet for long periods.

The link between the drug and the dramatic fall in raptor numbers was established in 2004 by a US-led team.